Harmful components such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) are present in exhaust gas that is emitted by internal combustion engines such as an automobile engine. Exhaust gas purification catalysts are conventionally used in order to remove efficiently such exhaust gas components. Exhaust gas purification catalysts adopt typically a form in which a noble racial functioning as a catalyst (hereafter also simply referred to as “catalyst metal”) is supported on a porous earner. Typical examples of catalyst metals include for instance noble metals of the platinum group such as platinum (Pt), rhodium (Rh), and palladium (Pd). However, these noble metals are expensive and also valuable as resources. Accordingly, it is preferable to reduce the use amount of catalyst metal from the viewpoint of saving energy and lowering costs. For instance Patent Literature 1 is an example of a relevant technology in this regard. Patent Literature 1 discloses an exhaust gas purification catalyst provided with a substrate having a plurality of through-holes in the direction of exhaust gas flow, and with a catalyst layer containing a noble metal, formed on the inner wall surface of the through-holes, wherein the thickness of the catalyst layer is adjusted so that the fluid pressure of exhaust gas is uniform among all the through-holes.